1. Field of the Invention
The present invention relates to a pulsed doppler radar system having a detection probability which is not reduced by a change in a frequency band of a receiving signal and a signal-to-noise ratio.
2. Prior Art
FIG. 1 is a block diagram showing the construction of a conventional pulsed doppler radar system as disclosed in "Air-borne Pulsed Doppler Radar" written by G. V. Morris and published by Artec House, Inc. in 1988. In the figure, a transmitter 2 is connected through a TR switch 4 to an antenna 6 which is in turn connected to a receiver 8. A signal received by the receiver 8 passes through an A/D converter 10 and is fed to a plurality M of range bins 12.sub.1 -12.sub.M. These range bins have their own numbers as shown in FIG. 1.
The signals output from the range bin 12.sub.1 are fed through a plurality L of doppler filters 14.sub.1 -14.sub.L to a plurality L of magnitude detectors 16.sub.1 -16.sub.L. The respective magnitude detectors are connected through a plurality L of non-coherent integrators 18.sub.1 -18.sub.L to a plurality L of threshold detectors 20.sub.1 -20.sub.L. The remaining signals belonging to the range bins 12.sub.2 -12.sub.M are processed in a manner similar to the above described. The outputs of the threshold detectors are fed to a display 22.
In operation, a transmitted signal is produced by the transmitter 2 and radiated from the antenna 6 toward a target. The transmitted signal is then reflected by the target and received by the antenna 6. The received signal is fed through the TR switch 4 to the receiver 8 where the received signal is converted to a complex video signal. The complex video signal is fed to the A/D converter 10 and converted to a digital signal thereby. The digital signal is separated and fed to M range bins 12.sub.1 -12.sub.M provided in accordance with M different ranges. These range bins output respective range signals. The range signal output from the range bin 12.sub.1 is fed to corresponding doppler filters 14.sub.1 -14.sub.L for the purpose of velocity measurement. These doppler filters effect coherent integration (pre-detection integration) of the range signal. The outputs of the doppler filters 14.sub.1 -14.sub.L are then magnitude-detected by the magnitude detectors 16.sub.1 -16.sub.L and subjected to non-coherent integration (post-detection integration) by the non-coherent integrators 18.sub.1 -18.sub.L. When the level of the output signals from the non-coherent integrators 18.sub.1 -18.sub.L exceeds threshold levels preset in the threshold detectors 20.sub.1 -20.sub.L, a target is detected and displayed on the display 22.
In such a conventional pulsed doppler radar system as described above, an integration number of coherent integration and an integration number of non-coherent integration are fixed regardless of any change in a frequency bandwidth of the doppler spectrum of a received signal (hereinafter called a "received signal frequency bandwidth") and a signal-to-noise ratio of the received signal. Assuming the coherent integration number to be Nc and the total number of pulse hits to be P, the non-coherent integration number is then equal to P/Nc. Therefore, such a conventional pulsed radar system constructed as described above has a problem of limited detection probability.